Study on layered perovskite cathodes for proton conducting solid oxide fuel cell

Abstract

In order to lower the operating temperature of the Solid oxide fuel cell, the NdBa1-xSrxCo2O5+d (x=0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1) layered perovskite oxides system has been applied for intermediate temperature solid oxide fuel cell and proton conducting solid oxide fuel cell in this study. For A-site, Nd is used which is briskly researched in CMR area. A’ site is substituted by Sr instead of Ba for increasing the ionic conductivity and improving the catalytic activity for the oxygen reduction reaction. For stability of structure and improving electric conductivity, Co is used for B-site. The cathode powders were synthesized by glycine nitrate process. Microstructure was no significant difference among powders by Scanning Electron Miscroscopy(SEM). The surface chemistry and chemical states of the layered perovskite oxides system has been studied using X-ray photoelectron Spectroscopy (XPS) and X-ray diffraction (XRD) in this study. The lattice parameter and unit cell volume were lowered as Sr contents increased due to smaller ion size of Sr. Substitution of Sr in oxides system reduces the binding energy of cations (Nd, Ba, Sr and Co). The substitution does not change the charge state of Nd and it has effect on the amount of SrCO3, SrO and BaCO3. Also, substitution leads to change the charge states of part of cobalt ion from Co3+ to Co4+ which increases high electrical conductivity. Three types of oxygen peaks were observed in the oxides system with lattice oxygen, carbonated species and adsorbed oxygen species with deconvolution results. The binding energy of O1s is relatively lower than conventional simple perovskite. Through electrochemical impedence analysis, NdBa0.5Sr0.5Co2O5+d shows lowest ASR values and has high reduction stability. The NdBa0.5Sr0.5Co2O5+d will be desirable cathode candidate for intermediate temperature solid oxide fuel cell, according to various aspects. Also, the cathode was applied to proton conducting electrolyte for symmetry cell w...